The present disclosure relates generally to a method of reusing material used in the manufacture of composite parts and, more particularly, to a method of reusing uncured prepreg scrap or remnant prepreg framework.
The composite market continues to grow as manufacturers in industries such as aerospace, automobile, sporting, and wind continue to seek ways of manufacturing parts that are stronger than traditional metallurgical parts, yet lighter in weight, thereby resulting in a reduction of CO2 emissions. In addition to their strength and weight benefits, composite materials also have the benefits of increased corrosion resistance, improved fire resistance, easier design because of functional integration, and the possibility of complex shapes. Because of these benefits of composite materials, their use will only increase.
Unfortunately, present composite manufacturing techniques generate a substantial amount of scrap or remnant uncured prepreg material from a sheet of prepreg material from which prepreg parts are cut. A sheet of prepreg material is known in the industry as prepreg broadgoods. The amount of scrap from prepreg broadgoods can be as much as 35%. This scrap is currently estimated to be produced in the amount of millions of pounds annually, and, especially if it is considered to be a hazardous waste, can be costly for manufacturers to dispose of Uncured epoxy resin is the hazardous component of the waste prepreg. Direct exposure to uncured epoxy resin can cause sensitization by skin contact and irritation to eyes and skin. Furthermore, epoxy-based materials are toxic to aquatic organisms and many cause long-term adverse effects in the aquatic environment. Waste disposal fees, typically $0.75 to $3 per pound of scrap, and exponentially higher if the waste is considered hazardous, represent a loss of revenue as the fiber and uncured resin in the scrap are still usable. Virgin carbon fiber prepreg material typically costs around $45 per pound. Upcycling of scrap prepreg can help companies recover some of their material and manufacturing costs as well as be environmentally friendly.
For the present disclosure, the term “reuse” refers to virgin or uncured prepreg or composite material, whereas “recycle” refers to cured prepreg or composite materials. Different techniques and applications have been developed for recycling prepreg material. The composite can be ground, sheared, chipped or flaked into suitable sizes for use as filler material in new molded composite parts.
Likewise, various methods and applications have been developed for reusing prepreg material. For example, one technique involves reducing the random shapes and cut-outs of scrap prepreg into rectangular chip form. This cut prepreg scrap can be directly used to manufacture parts through closed compression molding, or it can be further processed into a sheet form through the application of heat and pressure and be made available as rolls. See W. Michaeli et al., “New Technologies for Processing of Non-Cured Prepreg Waste—Preparation of High Strength DMC”, 41st International SAMPE Symposium, Mar. 24-28, 1996.
Still, virgin prepreg is commonly supplied with an interleaf (or a releasable backing sheet) on one or both sides of the prepreg. Uncured prepreg is typically tacky to the touch and without the interleaf backing the uncured prepreg material, would stick together when rolled up for shipping. This interleaf, which can be in the form of, for example, a polyethylene or paper sheet, needs to be removed in order for the uncured prepreg scrap to be reused. This is typically done by hand. Therefore, there remains a need for a less laborious process of preparing prepreg material for reuse.
Recycling cured prepregs is difficult due to both the reinforcing fiber and the resin. As a result, recycling is limited to down recycling. Y. Yang et al., “Recycling of Composite Materials”, Chem. Eng. Process (2011).